First detection of gas in a circumplanetary disk

Scientists using the Atacama Large Millimeter/submillimeter Array (ALMA) and partners at the National Radio Astronomy Observatory (NRAO) have succeeded in detecting gas in a circumplanetary disk for the first time. In addition, the discovery also points to the presence of a very young exoplanet. The research results will be published in The Letters of the Astrophysical Journal.

Circumplanetary disks are accumulations of gas, dust, and debris around young planets. These discs give rise to moons and other small, rocky objects, and control the growth of young, giant planets. Studying these disks in their earliest stages can help shed light on the formation of our own solar system, including the Galilean moons of Jupiter, which scientists believe formed in a circumplanetary disk of Jupiter about 4.5 billion years ago to have.

While studying AS 209, a young star located about 395 light-years from Earth in the constellation Ophiuchus, scientists observed a patch of emitted light at the center of an otherwise empty gap in the gas surrounding the star. This led to the discovery of the circumplanetary disk surrounding a potential Jupiter-mass planet.

Scientists are watching the system closely, both because of the planet’s distance from its star and because of the star’s age. The exoplanet is more than 200 astronomical units, or 18.59 billion miles, from the host star, challenging currently accepted theories of planet formation. And if the host star’s estimated age of just 1.6 million years is correct, this exoplanet could be one of the youngest ever discovered. More research is needed, and scientists hope upcoming observations with the James Webb Space Telescope will confirm the planet’s presence.

“The best way to study planet formation is to watch planets as they form. We live in a very exciting time where this is happening thanks to powerful telescopes like ALMA and JWST,” said Jaehan Bae, professor of astronomy at the University of Florida and lead author of the article.

Scientists have long suspected the presence of circumplanetary disks around exoplanets, but were unable to prove this until recently. In 2019, ALMA scientists made the first-ever discovery of a circumplanetary lunar-forming disk while observing young exoplanet PDS 70c, and confirmed the find in 2021. The new observations of gas in a circumplanetary disk at AS 209 could shed more light on the evolution of planetary atmospheres and the processes by which moons form.